Urinary stress incontinence arises when an increase in abdominal pressure, such as from laughing, coughing, lifting, or exercise, results in urinary leakage. Normally, the urethra, which is the urinary lumen which passes urine from the bladder, will not leak with ordinary increases in abdominal pressure, also referred to as stress. However there are two conditions, referred to as type II and type III that commonly lead to incontinence.
Type II incontinence, also referred to as hypermobility, occurs when the support structures of the pelvic floor have been weakened, for instance from childbirth. This allows the bladder to descend below its normal location in the abdominal cavity and the bladder neck, where it joins the urethra, to funnel open under increased abdominal pressure.
Type II incontinence has most often been treated by a class of surgical procedures called suspensions of which there are many variations. Variations such as the Marshal-Marchetti-Krantz or the Burch procedures are quite invasive, requiring an abdominal incision. Other variations, generally called needle suspensions and including the Stamey and Raz procedures, are less invasive and may be done on an outpatient basis. Generally these procedures place sutures into tissue on either side of the urethra near the bladder neck and then lift or suspend the urethra and bladder from a higher anchoring point such the pubic bone, coopers ligament or the rectus abdominis muscle. This support compensates for weakness of the pelvic floor.
Unfortunately it has been found that these procedures, especially the needle suspensions, often fail over time because the sutures pull through the tissue on either side of the bladder neck or the tissue continues to sag between these points. Another concern is that if the bladder neck is lifted too high the patient may be put into urinary obstruction. Still another concern is that too much elevation may induce urge incontinence where the patient feels a need to urinate even when the bladder is not full. These later conditions may not be detected until after the surgery and the patient is up and around. In order to address some of these problems U.S. Pat. Nos. 4,938,760 and 4,969,892 propose a mechanism for allowing postoperative adjustment to the degree of suspension.
The other common cause of stress incontinence, type III also called intrinsic sphincter deficiency, occurs when the urinary sphincter which controls flow of urine from the bladder is dysfunctional. This may be caused by trauma, urethral scarring or any of a number of neurological conditions. For type III incontinence the most common treatment has been a class of surgical procedures called slings.
Generally a sling or strap of material is placed between the urethra and vagina and the ends are attached to the same selection of higher anchoring points as for a suspension procedure. Pressure of the sling on the underside of the urethra causes closing or coaptation of the urethra to compensate for the dysfunctional sphincter. Another way to achieve coaptation would be to provide an expandable element or elements such as balloons on the sling underneath or alongside the urethra. The sling may be made from artificial material such as polypropylene mesh, autologous tissue harvested from the patient such as rectus fascia, or cadaveric fascia latta.
While originally intended to provide coaptation for treating type III incontinence it has been recognized that slings also provide the support function sought by suspension procedures. While slings are somewhat more invasive than needle suspensions, they provide more reliable support since the sling is a continuous piece of material that goes underneath the urethra rather than being attached to fallible tissue alongside. At the same time it has also been recognized that mast stress incontinent patients do not have pure type II or type III but rather some of both. Often treating one of these conditions will unmask the presence of the other.
For these reasons surgeons are more and more turning to slings to treat both types of stress incontinence. Nevertheless slings are still prone to some of the same problems as suspensions. Often it is not possible to tell if there has been enough coaptation or suspension to provide continence without urinary obstruction before the patient has recovered. Another problematic disorder which may result from the foregoing procedures is called “postsurgical urgency,” which is caused by improperly applied pressure to the periurethral tissues in which innervation is very dense causing hyperactivity of the bladder and urethra. This disorder causes the patient to feel an urgency to void when their bladder does not require voiding. Amelioration of the foregoing problems generally entails a second open surgical procedure to reduce the pressure on the bladder neck and proximal urethra. Thus, there is a need in the art for an improved sling for the treatment of urinary stress incontinence.